Jasonが参照している記事が示唆しているように、ページングが重要です。これは、特定のフォルダー内のすべての電子メールのリストを取得するためにOffice365 Exchange Serverに対して使用しているコードです(20,000を超える電子メール、ページサイズ100で非常に高速に動作します)。
// via https://msdn.microsoft.com/en-us/library/office/dn592093(v=exchg.150).aspx
int pageSize = 100;
int offset = 0;
ItemView view = new ItemView(pageSize + 1, offset);
view.PropertySet = new PropertySet(ItemSchema.Subject, ItemSchema.DateTimeSent);
view.OrderBy.Add(ItemSchema.DateTimeReceived, SortDirection.Descending);
view.Traversal = ItemTraversal.Shallow;
bool moreItems = true;
ItemId anchorId = null;
while (moreItems)
{
FindItemsResults<Item> results = service.FindItems(buildsFolderId, view);
moreItems = results.MoreAvailable;
if (moreItems && anchorId != null)
{
// Check the first result to make sure it matches
// the last result (anchor) from the previous page.
// If it doesn't, that means that something was added
// or deleted since you started the search.
if (results.Items.First<Item>().Id != anchorId)
{
Console.Error.WriteLine("The collection has changed while paging. Some results may be missed.");
}
}
if (moreItems)
{
view.Offset += pageSize;
}
anchorId = results.Items.Last<Item>().Id;
// Because you’re including an additional item on the end of your results
// as an anchor, you don't want to display it.
// Set the number to loop as the smaller value between
// the number of items in the collection and the page size.
int displayCount = results.Items.Count > pageSize ? pageSize : results.Items.Count;
for (int i = 0; i < displayCount; i++)
{
Item item = results.Items[i];
Console.WriteLine("[" + item.DateTimeSent + "] " + item.Subject);
}
Console.Error.WriteLine("Current offset: {0}/{1}", view.Offset, folder.TotalCount);
}